Radio terminal, radio base station, channel signal forming method, and channel signal receiving method

ABSTRACT

A base station communicates with a terminal, for which an uplink component carrier and downlink component carriers are configured. The base station adjusts a payload size of control information, transmitted in a downlink control channel, based on a basic payload size, and maps the control information onto a search space in at least one of the downlink component carriers. The basic payload size of the control information mapped onto a search space in a primary downlink component carrier is based on a number of information bits obtained from a bandwidth of the primary downlink component carrier, and on a number of information bits obtained from a bandwidth of the uplink component carrier. The basic payload size of the control information mapped onto a search space in a non-primary downlink component carrier is based on a number of information bits obtained from a bandwidth of the non-primary downlink component carrier.

TECHNICAL FIELD

The present invention relates to a radio terminal, radio base station,channel signal forming method and channel signal reception method.

BACKGROUND ART

In 3GPP LTE, OFDMA (Orthogonal Frequency Division Multiple Access) isemployed as a downlink communication method. In a radio communicationsystem adopting 3GPP LTE, a base station transmits a synchronizingsignal (synchronization channel: SCH) and a broadcast signal (broadcastchannel: BCH) using prescribed communication resources. A terminal firstsynchronizes with a base station by capturing the SCH. Then, theterminal acquires parameters that are specific to that base station (forexample, a frequency bandwidth) by reading BCH information (see, forexample, Non-patent Literature 1, 2 and 3).

Also, after acquiring base station-specific parameters, a terminal tosupport an LTE system (hereinafter “LTE terminal”) sends a connectionrequest to the base station, and, by this means, establishescommunication with the base station. The base station transmits controlinformation to the terminal with which communication has beenestablished, by using a PDCCH (Physical Downlink Control CHannel) whennecessary.

The terminal performs “blind detection” for a received PDCCH signal.That is, a PDCCH signal includes a CRC (Cyclic Redundancy Check) part,and, at a base station, this CRC part is masked by the terminal ID ofthe target terminal. Thus, until a terminal demasks the CRC part of areceived PDCCH signal with the terminal's terminal ID, the terminalcannot decide whether or not the PDCCH signal is for that terminal. Inthis blind detection, if the result of demasking is that CRC calculationis OK, the PDCCH signal is decided to have been sent to the terminal.

Also, control information sent from a base station includes assignmentcontrol information including such as information about resources whicha base station assigns to a terminal. A terminal needs to receive bothdownlink assignment control information and uplink assignment controlinformation which have a plurality of formats. Although downlinkassignment control information which a terminal should receive can bedefined in a plurality of sizes depending on the transmission antennacontrol method and frequency assignment method at a base station, someof these downlink assignment control information formats (hereinaftersimply referred to as “downlink assignment control information”) anduplink assignment control information formats (hereinafter simplyreferred to as “uplink assignment control information”) are transmittedusing PDCCH signals having the same size. A PDCCH signal includes typeinformation of assignment control information (for example, a 1 bitflag). Thus, even if the size of a PDCCH signal including downlinkassignment control information and the size of a PDCCH signal includinguplink assignment control information are the same, a terminal checkstype information of assignment control information, and by this meanscan distinguish between downlink assignment control information anduplink assignment control information. The PDCCH format to transmituplink assignment control information is PDCCH format 0, and the PDCCHformat to transmit downlink assignment control information, transmittedin a PDCCH signal being the same size as uplink assignment controlinformation, is PDCCH format 1A.

However, cases might occur where the information size of uplinkassignment control information determined from the uplink bandwidth(that is, the number of bits required for transmission) and theinformation size of downlink assignment control information determinedfrom the downlink bandwidth differ. To be more specific, if an uplinkbandwidth is small, the information size of uplink assignment controlinformation becomes small, and, if a downlink bandwidth is small, theinformation size of downlink assignment control information becomessmall. If a difference of bandwidths results in a difference ofinformation sizes like this, by adding zero information to the smallerassignment control information (that is, by performing zero-padding),the size of downlink assignment control information and the size ofuplink assignment control information are made equal. By this means,whether the content is downlink assignment control information or uplinkassignment control information, PDCCH signals have the same size.

The size adjustment of control information as mentioned above reducesthe number of times of blind detection at a terminal on the receptionside. However, when a downlink transmission bandwidth of a base stationis wide, the base station transmits many PDCCH signals at once, so thatthe terminal cannot reduce enough the number of times of blind detectionin its normal operation, and the increase of circuit scale of a terminalcauses a problem.

Therefore, to further reduce the number of times of blind detection by aterminal, a terminal employs the method to limit a physical space wherea terminal receives control information. Thus, each terminal is reportedin advance the time and frequency space where control information forthat terminal is likely to be included, and performs blind detectiononly in a terminal-specific space where control information for thatterminal is likely to be included. This terminal-specific physical spaceis called “UE specific search space (UE SS).” This UE specific searchspace is associated with, for example, a terminal ID. Also, a time andfrequency interleaving is employed to provide a nearly equal timediversity and frequency diversity effect in all UE specific searchspaces.

Meanwhile, a PDCCH signal includes control information that is reportedat once to a plurality of terminals (for example, scheduling informationabout downlink broadcast signals). To transmit this control information,a physical space that is common to all LTE terminals that should receivethe target downlink broadcast signal, called “common search space(Common SS),” is prepared in a PDCCH signal. Even in this common searchspace, as in the UE specific search space, an information sizeadjustment is performed between the size of downlink assignment controlinformation and the size of uplink assignment control information. Thus,even in common search space, it is possible to transmit uplinkassignment control information to the terminal without increasing thenumber of times of blind detection by the terminal.

Thus, a terminal requires both control information included in a UEspecific search space and control information included in a commonsearch space, so that the terminal needs to perform blind detection forall uplink control information and downlink control information includedin the UE specific search space and uplink control information anddownlink control information included in the common search space.

FIG. 1 shows the transmissions of PDCCH signals by format 0 and format1A. In FIG. 1, as mentioned above, in each UE specific search space andcommon search space, PDCCH signals are transmitted by format 0 andformat 1A. In FIG. 1, the downlink bandwidth is 15 MHz and the uplinkbandwidth is 20 MHz. The size of assignment control information dependson the bandwidth, so that, when comparing the information size (the sizeof format 1A) required for the downlink assignment decided from thedownlink bandwidth and the information size (the size of format 0)required for the uplink assignment decided from the uplink bandwidth,the latter is larger. Thus, the pairs of a downlink band and an uplinkband are used between the base station and the terminal as shown in FIG.1, zero padding is performed to the downlink assignment controlinformation to adjust the size of format 1A to the size of format 0.

Also, the standardization of 3GPP LTE-advanced has been started torealize faster communication than 3GPP LTE. A 3GPP LTE-advanced system(hereinafter referred to as “LTE-A system”) follows a 3GPP LTE system(hereinafter referred to as “LTE system”). In 3GPP LTE-advanced, torealize a downlink transmission speed equals or exceeds maximum 1 Gbps,a base station and a terminal which can communicate in widebandfrequency of 40 MHz or more are expected to be introduced.

With an LTE-A system, to realize a communication by ultra fasttransmission speed that is several times as fast as transmission speedin an LTE system, and backward compatibility for the LTE system at thesame time, a band for the LTE-A system is divided into “component bands”that are LTE supporting bandwidths and that are equal to or lower than20 MHz. “Component band” is a bandwidth for maximum 20 MHz here and isdefined as the basic unit of a communication band. Furthermore,“component band” in a downlink (hereinafter referred to as “downlinkcomponent band”) is defined as a band separated by downlink frequencybandwidth information in a BCH broadcasted from a base station, or aband defined by the range of distribution when a downlink controlchannel (PDCCH) is arranged in a distributed manner. Also, “componentband” in an uplink (hereinafter referred to as “uplink component band”)is defined as a band separated by uplink frequency bandwidth informationin a BCH broadcasted from a base station, or the basic unit of acommunication band of 20 MHz or less including a PUSCH (Physical UplinkShared CHannel) near the center, and a PUCCH for an LTE on both ends.Also, in 3GPP LTE-Advanced, “component band” may be designated as“Component Carrier(s)” in English.

In an LTE-A system, the communication using the bandwidth that bundles afew of these component bands, so-called “Carrier aggregation” issupported. Generally, throughput requirements for an uplink and adownlink are different, so that in an LTE-A system, studies are underwayto use the carrier aggregation in which the number of component bandsset for an arbitrary terminal (hereinafter “LTE-A terminal”) associatedwith the LTE-A system, so-called “asymmetric carrier aggregation.”Furthermore, the case will also be supported where the numbers ofcomponent bands are asymmetric between an uplink and a downlink, andwhere all component bands have different frequency bandwidths.

FIGS. 2A-B show an asymmetric carrier aggregation applied to a dedicatedterminal and its control sequence. FIGS. 2A-B show an example in whichthe bandwidths and the numbers of component bands of an uplink and adownlink of the base station are symmetric.

In FIGS. 2A-B, although as for terminal 1, a configuration is carriedout to perform the carrier aggregation using two downlink componentbands and one uplink component band of the left side, as for terminal 2,a configuration is carried out to use the uplink component band of theright side for the uplink communication, even though a configuration iscarried out to use the same two downlink component bands as in terminal1.

When focusing on terminal 1, between the LTE-A base station and theLTE-A terminal that form an LTE-A system, the transmission and receptionof signals are performed according to the sequence diagram shown in FIG.2A. As shown in FIG. 2A, (1) when starting communication with a basestation, terminal 1 synchronizes with the left side downlink componentband and reads from broadcast signals called SIB2 (System InformationBlock Type 2), the information of an uplink component band that forms apair with the left side downlink component band. (2) By using thisuplink component band, terminal 1, for example, sends a connectionrequest to the base station, and by this means starts communication withthe base station. (3) When determining that a plurality of downlinkcomponent bands need to be assigned to a terminal, the base stationcommands the terminal to add downlink component bands. However, in thiscase, the number of an uplink component band does not increase, andasymmetric carrier aggregation starts in terminal 1, that is a dedicatedterminal

CITATION LIST Non-Patent Literature

NPL 1

-   3GPP TS 36.211 V8.5.0, “Physical Channels and Modulation (Release    8),” December 2008    NPL 2-   3GPP TS 36.212 V8.5.0, “Multiplexing and channel coding (Release    8),” December 2008    NPL 3-   3GPP TS 36.213 V8.5.0, “Physical layer procedures (Release 8),”    December 2008

SUMMARY OF INVENTION Technical Problem

Meanwhile, as mentioned above, in FIGS. 2A-B, one uplink component band(which is in the left side) and two downlink component bands areconfigured to terminal 1. Thus, as for terminal 1, both two downlinkcomponent bands are associated with the left side uplink component band.As shown in FIG. 3, regardless of the PDCCH signal of whichever downlinkcomponent band the base station uses to transmit an uplink assignmentcontrol signal (format 0) to terminal 1, terminal 1 transmits a PUSCH(Physical Uplink Shared CHannel) in the left uplink component band.Thus, to transmit, in the right downlink component band, assignmentcontrol information (format 0) of the left uplink component band anddownlink assignment control information (format 1A) of the downlinkcomponent band, to terminal 1, and to reduce the number of times ofblind detection of terminal 1, the base station has to determine thisinformation size in accordance with the left side uplink componentbandwidth and the right side downlink component bandwidth.

However, a broadcast signal transmitted in the right downlink componentband (for example, D-BCH) is necessary for both an LTE-A terminal and anLTE terminal. Thus, scheduling information about that broadcast signal(which is informed by format 1A) has to be able to be received by an LTEterminal. Thus, given that the reception of a broadcast signal that isnecessary for both an LTE-A terminal and an LTE terminal, it isnecessary to compare the information size determined by the bandwidth ofa downlink component band in which this broadcast signal is transmitted,and the information size determined by the bandwidth of the uplinkcomponent band which is made as a pair with this downlink component bandin an LTE system, and to perform zero padding using the larger one asthe size adjustment reference.

Although assignment control information of the left uplink componentband has to be transmitted in the right side downlink component band asabove, without making both an LTE-A terminal and an LTE terminal havedifficulty reception broadcast signals and without increasing the numberof times of blind detection on the LTE-A terminal, it is difficult torealize.

It is therefore an object of the present invention to provide a radioterminal, radio base station, channel signal forming method and channelsignal reception method to reduce the number of times of blind detectionin a reception process of assignment control information without causingany problems on reception broadcast signals.

Solution to Problem

One aspect of the radio base station of the present invention that has aplurality of uplink component bands and a plurality of downlinkcomponent bands as a communication band for the radio base station, setsfor each radio terminal a component band group formed with the uplinkcomponent band in the communication band and a plurality of downlinkcomponent bands associated with the uplink component band, and is ableto communicate with the radio terminal using the component band group,the radio base station employs a configuration having: a forming sectionthat forms for each downlink component band the first channel signalthat has a common search space that is common among a plurality of radioterminals and a user equipment specific search space that isindividually assigned to each radio terminal; and an information sizeadjusting section that adjusts information sizes of uplink controlinformation and downlink control information that are to be sent to anarbitrary transmission target terminal and that are included in theformed first channel signal, based on the size adjustment reference, inthe common search space of a downlink additional component band that isincluded in the component band group, the downlink additional componentband being not a basic component band that is a downlink component bandin the component band group, and that is a downlink component band inwhich a broadcast channel signal that includes information about theuplink component band of the component band group is transmitted, using,as a common size adjustment reference among a plurality of radioterminals, the larger one of: the information size of downlinkassignment control information determined from the bandwidth of thedownlink additional component band; and the information size of uplinkassignment control information determined from the bandwidth of theuplink component band that is associated with the downlink additionalcomponent band in the broadcast channel signal transmitted in thedownlink additional component band, and in the user equipment specificsearch space of the downlink additional component band, using, as thesize adjustment reference for each radio terminal, the larger one of theinformation size of downlink assignment control information determinedfrom the bandwidth of the downlink additional component band and theinformation size of uplink assignment control information determinedfrom the bandwidth of the uplink component band.

One aspect of the radio terminal of the present invention that is ableto communicate with a radio base station by using a component band groupthat includes an uplink component band and a plurality of downlinkcomponent bands associated with the uplink component band and that isset by the radio base station, the radio terminal employs aconfiguration having: a radio reception section that has a common searchspace that is common among a plurality of ration terminals and a userequipment specific search space that is individually assigned to eachradio terminal and that receives from each downlink component band thefirst channel signal that includes uplink assignment control informationor downlink assignment control information; a determining section thatdetermines the basic information size to use for a reception process ofthe first channel signal of each downlink component band; and a channelsignal reception process section that performs the reception process ofthe first channel signal based on the basic information size, where inthe common search space of a downlink additional component band that isincluded in the component band group, the downlink additional componentband being not a basic component band that is a downlink component bandin the component band group that is set for the radio terminal, and thatis a downlink component band in which a broadcast channel signal thatincludes information about the uplink component band of the componentband group is transmitted, the determining section determines the basicinformation size based on the larger one of: the information size ofdownlink assignment control information determined from the bandwidth ofthe downlink additional component band; and the information size ofuplink assignment control information determined from the bandwidth ofthe uplink component band that is associated with the downlinkadditional component band in the broadcast channel signal transmitted inthe downlink additional component band; and in the user equipmentspecific search space of the downlink additional component band, thedetermining section determines the basic information size based on thelarger one of the information size of downlink assignment controlinformation determined from the bandwidth of the downlink additionalcomponent band and the information size of uplink assignment controlinformation determined from the bandwidth of the uplink component band.

One aspect of the channel signal forming method of the present inventionthat forms a channel signal for each downlink component band included ina component band group formed by an uplink component band and aplurality of downlink component bands associated with the uplinkcomponent band, the method includes the steps of: forming for eachdownlink component band the first channel signal that has a commonsearch space that is common among a plurality of radio terminals and auser equipment specific search space that is individually assigned toeach radio terminal; and adjusting information sizes of uplinkassignment control information and downlink assignment controlinformation that are included in the formed first channel signal, basedon the size adjustment reference, where in the common search space of adownlink additional component band that is included in the componentband group, the downlink additional component band being not a basiccomponent band that is a downlink component band in the component bandgroup, and that is a downlink component band in which a broadcastchannel signal that includes information about the uplink component bandof the component band group is transmitted, the larger one of: theinformation size of downlink assignment control information determinedfrom the bandwidth of the downlink additional component band; and theinformation size of uplink assignment control information determinedfrom the bandwidth of the uplink component band that is associated withthe downlink additional component band in the broadcast channel signaltransmitted in the downlink additional component band, is determined asthe common size adjustment reference among a plurality of radioterminals, and in the user equipment specific search space of thedownlink additional component band, the larger one of the informationsize of downlink assignment control information determined from thebandwidth of the downlink additional component band and the informationsize of uplink assignment control information determined from thebandwidth of the uplink component band, is determined as the sizeadjustment reference for each radio terminal.

One aspect of the channel signal reception method of the presentinvention that receives a channel signal of each downlink component bandincluded in the component band group formed by an uplink component bandand a plurality of downlink component bands associated with the uplinkcomponent band, the method includes the steps of: receiving via radiothe first channel signal that includes uplink assignment controlinformation or downlink assignment control information, while having acommon search space that is common among a plurality of radio terminalsand a user equipment specific search space that is individually assignedto each radio terminal; determining the basic information size to usefor reception process of the first channel signal of each downlinkcomponent band; and performing reception process of the first channelsignal based on the basic information size, where in a common searchspace of a downlink additional component band that is included in thecomponent band group, the downlink additional component band being not abasic component band that is a downlink component band in the componentband group that is set for the radio terminal, and that is a downlinkcomponent band in which a broadcast channel signal that includesinformation about the uplink component band of the component band groupis transmitted, the basic information size is determined based on thelarger one of: the information size of downlink assignment controlinformation determined from the bandwidth of the downlink additionalcomponent band; and the information size of uplink assignment controlinformation determined from the bandwidth of the uplink component bandthat is associated with the downlink additional component band in thebroadcast channel signal transmitted in the downlink additionalcomponent band, and in a user equipment specific search space of thedownlink additional component band, the basic information size isdetermined based on the larger one of the information size of downlinkassignment control information determined from the bandwidth of thedownlink additional component band and the information size of uplinkassignment control information determined from the bandwidth of theuplink component band.

Advantageous Effects of Invention

The present invention provides a radio terminal, radio base station,channel signal forming method and channel signal reception method toreduce the number of times of blind detection in a reception process ofassignment control information without causing any problems on receivingbroadcast signals.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows transmissions of PDCCH signals by format 0 and format 1A;

FIGS. 2A-B show an asymmetric carrier aggregation, applied to adedicated terminal, and its control sequence;

FIG. 3 shows an asymmetric carrier aggregation applied to a dedicatedterminal;

FIG. 4 is a block diagram showing a configuration of a base stationaccording to an embodiment of the present invention;

FIG. 5 is a block diagram showing a configuration of a terminalaccording to an embodiment of the present invention;

FIG. 6 shows operations of a base station and a terminal; and

FIG. 7 shows operations of a base station and a terminal.

DESCRIPTION OF EMBODIMENTS

Now, an embodiment of the present invention will be explained in detailwith reference to the accompanying drawings.

FIG. 4 is a block diagram showing a configuration of base station 100according to an embodiment of the present invention. In FIG. 4, basestation 100 includes control section 101, PDCCH generating section 102,information size adjusting section 103, CRC (Cyclic Redundancy Check)adding section 104, modulating sections 105 and 106, SCH/BCH generatingsection 107, multiplexing section 108, IFFT section 109, CP addingsection 110, RF transmission section 111, RF reception section 112, CPremoving section 113, FFT section 114, extracting section 115, IDFTsection 116, and data reception section 117. Base station 100 isconfigured to be able to communicate with terminal 200 (described later)using a component band group composed of an uplink component band and aplurality of downlink component bands associated with the uplinkcomponent band. The component band group is set for every terminal 200and is noticed to terminal 200 in advance. Some or all of a plurality ofcomponent bands composing the component band group assigned to firstterminal 200 may overlap with constituent component bands of thecomponent band group assigned to second terminal 200.

Control section 101 generates control information (including uplinkassignment control information and downlink assignment controlinformation) and space assignment information indicating to which one ofa UE specific search space or a common search space each piece ofcontrol information is assigned. This control information includescomponent band group setting information individually assigned to eachterminal 200, “basic component band information” (described later),dedicated assignment control information, such as resource assignmentinformation in component bands composing a component band group, andcommon assignment control information which is common to all terminals200 that receive broadcast signals from the target component band. WhileUE specific search space assignment control information is generated forcontrol information to be assigned to each terminal 200 on a dedicatedbasis, common search space assignment information is generated forcommon control information that is common for all terminals 200.

A downlink component band that is set for arbitrary terminal 200 bycontrol section 101, and in which a BCH, which broadcasts theinformation about an uplink component band forming the component bandgroup informed to terminal 200 in advance, is transmitted, is “basiccomponent band” for the target terminal, and the information about thisbasic component band is the above “basic component band information.”Arbitrary terminal 200 reads BCH information, and by this means thisbasic component band information can be recognized.

Control section 101 outputs to information size adjusting section 103information size comparing information 1 that shows the comparinginformation sizes of downlink assignment control information determinedby the bandwidth of the basic component band and uplink assignmentcontrol information determined by the bandwidth of an uplink componentband, and information size comparing information 2 that shows thecomparing information sizes of downlink assignment control informationdetermined by the bandwidth of a downlink component band other than thebasic component band and uplink assignment control informationdetermined by the bandwidth of an uplink component band.

PDCCH generating section 102 receives control information and spaceassignment information generated in control section 101, and generates aPDCCH signal subject to be sent in each downlink component band, basedon these control information and space assignment information.

Also, while mapping common assignment control information to the commonsearch space of each PDCCH signal, PDCCH generating section 102 mapsdedicated assignment control information to a UE specific search space.This process of sorting common assignment control information anddedicated assignment control information is performed based on spaceassignment information.

Information size adjusting section 103 receives control information andspace assignment information generated in control section 101. Based onthese control information and space assignment information, informationsize adjusting section 103 adjusts the information size of uplinkassignment control information and downlink assignment controlinformation included in PDCCH signals received from PDCCH generatingsection 102.

Specifically, based on basic component band information, informationsize adjusting section 103 determines whether a PDCCH signal subject toinformation size adjustment should be transmitted in the basic componentband or in a different downlink component band.

In the common search space of the first PDCCH signal which is sent in adownlink component band other than the basic component band, informationsize adjusting section 103 uses the larger one of the information sizeof downlink assignment control information determined from the bandwidthof the target downlink component band in which the first PDCCH signal issent, and the information size of uplink assignment control informationdetermined from the bandwidth of an uplink component band (which is notnecessarily included in the component band group for terminal 200)associated by broadcast signals in the target downlink component band,as a size adjustment reference, and, based on this size adjustmentreference, information size adjusting section 103 adjusts theinformation sizes of uplink assignment control information and downlinkassignment control information. However, the common search space of thefirst PDCCH signal is a common search space for a plurality of terminals200 that should receive the broadcast signal in the target componentband. In the UE specific search space of the first PDCCH signal,information size adjusting section 103 uses the larger one of theinformation size of downlink assignment control information determinedfrom the bandwidth of the target downlink component band in which thefirst PDCCH signal is sent, and the information size of uplinkassignment control information determined from the bandwidth of anuplink component band in the component band group of terminal 200, as asize adjustment reference, and, based on this size adjustment reference,information size adjusting section 103 adjusts the information sizes ofuplink assignment control information and downlink assignment controlinformation. However, a UE specific search space of the first PDCCHsignal is a space that, for example, associated with terminal ID and setfor every terminal 200.

Meanwhile, as for the second PDCCH signal (that is, a PDCCH signalincludes both uplink assignment control information and downlinkassignment control information) subject to be sent in the basiccomponent band, both in the common search space and the UE specificsearch space, information size adjusting section 103 uses the larger oneof the information size of downlink assignment control informationdetermined from the bandwidth of the target downlink component band inwhich the second PDCCH signal is sent, and the information size ofuplink assignment control information determined from the bandwidth ofan uplink component band in the component band group of terminal 200, assize adjustment reference, and, based on this size adjustment reference,information size adjusting section 103 adjusts the information sizes ofuplink assignment control information and downlink assignment controlinformation.

To be more specific, information size adjusting section 103 includes apadding section (not shown) to adjust the information size of controlinformation by adding zero information to control information. Thispadding section adds zero information to the smaller information sizeuntil the information sizes of downlink assignment control informationand uplink assignment control information have equal information size.To which one of downlink assignment control information and uplinkassignment control information zero information is added is determinedbased on information size comparing information.

Also, in the common search space of the first PDCCH signal, the paddingsection adds zero information to uplink assignment control informationor downlink assignment control information, until it becomes equal tothe target information size determined from the larger one of theinformation size of downlink assignment information determined from thebandwidth of the target downlink component band in which the first PDCCHsignal is sent, and the information size of uplink assignment controlinformation determined from the bandwidth of the uplink component band(which is not necessarily included in the component band group ofterminal 200) associated by the broadcast signal in the target downlinkcomponent band. Also, in the UE specific search space of the first PDCCHsignal, the padding section adds zero information to uplink assignmentcontrol information or downlink assignment control information, until itbecomes equal to the target information size determined from the largerone of the information size of downlink assignment informationdetermined from the bandwidth of the target downlink component band, andthe information size of uplink assignment control information determinedfrom the bandwidth of the uplink component band of the component bandgroup of terminal 200.

Here, even if the downlink component band of first terminal 200 and thedownlink component band of second terminal 200 overlap, uplink componentbands included in the component band group of each terminal may bedifferent. In other words, even if the downlink component band of firstterminal 200 and the downlink component band of second terminal 200overlap, the overlapped downlink component band may be the basiccomponent band for first terminal 200 and may be a component band otherthan the basic component band for second terminal 200.

For this reason, the information size adjustment process of uplinkassignment control information and downlink assignment controlinformation in information size adjusting section 103 is performed foreach piece of assignment control information included in the targetPDCCH signal, based on the reference applied to destination terminal 200of the assignment control information.

CRC adding section 104 adds a CRC bit to a PDCCH signal whose size isadjusted in information size adjusting section 103, and then masks theCRC bit with a terminal ID. However, scheduling information related tothe broadcast signals which a plurality of terminals need to receive ismasked by an ID (that is, a common ID) that is set in common between aplurality of terminals. Then, CRC adding section 104 outputs the maskedPDCCH signal to modulating section 105.

Modulating section 105 modulates a PDCCH signal input from CRC addingsection 104, and outputs the modulated PDCCH signal to multiplexingsection 108.

Modulating section 106 modulates input transmission data (that isdownlink channel data), and outputs modulated transmission data signalsto multiplexing section 108.

SCH/BCH generating section 107 generates a SCH and a BCH, and outputsthe generated SCH and BCH to multiplexing section 108.

Multiplexing section 108 multiplexes the PDCCH signal input frommodulating section 105, the data signal (that is, a PDSCH signal) inputfrom modulating section 106, and the SCH and BCH input from SCH/BCHgenerating section 107. Based on the terminal ID input from controlsection 101 and downlink assignment control information associated withthe target terminal ID, multiplexing section 108 maps a data signal (aPDSCH signal) for terminal 200 associated with the terminal ID to adownlink component band.

Also, multiplexing section 108 maps the PDCCH signal input frommodulating section 105, to the dedicated resource space and the commonresource space in the resource space assigned for a PDCCH. Specifically,the PDCCH signal associated with a data signal which only a certainterminal should receive, is mapped to the resource associated with theterminal ID of the target terminal in a dedicated resource space, andthe PDCCH signal associated with a data signal which a plurality ofterminals should receive at once, is mapped to the resource in thecommon resource space.

IFFT section 109 converts a multiplex signal into a time waveform, andCP adding section 110 acquires an OFDM signal by adding a CP to thistime waveform.

RF transmission section 111 performs a radio transmission process (suchas up-conversion and a digital-to-analog (D/A) conversion) to an OFDMsignal input from CP adding section 110, and transmits the resultthrough an antenna. Then, an OFDM signal including assignment controlinformation is sent.

RF reception section 112 performs a radio reception process (such as adown-conversion and an analog-to-digital (A/D) conversion) to a receivedradio signal which is received in a reception band through an antenna,and outputs the received signal to CP removing section 113.

CP removing section 113 removes the CP from the received signal, and FFTsection 114 converts the received signal, from which the CP has beenremoved, into a frequency domain signal.

Based on uplink assignment control information input from controlsection 101, extracting section 115 extracts uplink channel data from afrequency domain signal input from FFT section 114, and IDFT (InverseDiscrete Fourier Transform) section 116 converts the extracted signalinto a time domain signal and outputs the time domain signal to datareception section 117.

Data reception section 117 decodes the time domain signal input fromIDFT section 116. And data reception section 117 outputs decoded uplinkdata as received data.

FIG. 5 is a block diagram showing the configuration of terminal 200according to an embodiment of the present invention. In FIG. 5, terminal200 includes RF reception section 201, CP removing section 202, FFTsection 203, frame synchronization section 204, demultiplexing section205, broadcast signal reception section 206, information sizedetermination section 207, PDCCH reception section 208, formatdetermination section 209, PDSCH reception section 210, modulatingsection 211, DFT section 212, frequency mapping section 213, IFFTsection 214, CP adding section 215, and RF transmission section 216.

RF reception section 201 performs a radio reception process (such as adown-conversion and an analog-to-digital (A/D) conversion) to a receivedradio signal (in this case, an OFDM signal) which is received in areception band through an antenna, and outputs the received signal to CP(Cyclic Prefix) removing section 202.

CP removing section 202 removes the CP from the received signal, and FFT(Fast Fourier Transform) section 203 converts the received signal, fromwhich the CP has been removed, into a frequency domain signal. Thisfrequency domain signal is output to frame synchronization section 204.

While searching for a SCH included in a signal input from FFT section204, frame synchronization section 203 establishes synchronization(frame synchronization) with base station 100. Also, framesynchronization section 204 acquires a cell ID associated with asequence used for a SCH (a SCH sequence). That is, the same process as anormal cell search is performed in frame synchronization section 204.Also, to demultiplexing section 205, frame synchronization section 204outputs frame synchronization timing information showing a framesynchronization timing, and the signal input from FFT section 203.

Based on frame synchronization timing information input from framesynchronization section 204, demultiplexing section 205 demultiplexesthe signal input from frame synchronization section 204 into a broadcastsignal (that is, a BCH), a control signal (that is, a PDCCH signal), anda data signal (that is, a PDSCH signal). Demultiplexing section 205receives information about a downlink component band from broadcastsignal reception section 206, and extracts a PDCCH signal on a perdownlink component band basis based on this information.

Broadcast signal reception section 206 reads the contents of a BCH inputfrom demultiplexing section 205, and acquires information related to theconfiguration of the downlink band and uplink band of base station 100.Broadcast signal reception section 206 acquires, for example, thenumbers of downlink component bands, the identification number, and thebandwidths of each component band. Broadcast signal reception section206 acquires information related to an uplink component band included ina BCH assigned in a plurality of downlink component bands. Among aplurality of uplink component bands, broadcast signal reception section206 determines the downlink component band, in which a BCH that is asource of information about the uplink component band (that is, anuplink component band included in component band group that terminal 200should use) that terminal 200 informed from base station 100 in advanceshould use, is transmitted, as “basic component band” for terminal 200,and generates the basic component band information. Broadcast signalreception section 206 outputs acquired BCH information and the basiccomponent band information to information size determination section207, PDCCH reception section 208, and format determination section 209.

Information size determination section 207 receives a PDCCH signal fromdemultiplexing section 205, and determines the basic information size onperforming blind detection on this PDCCH signal. This basic informationsize is determined based on basic component band information receivedfrom broadcast signal reception section 206, and the bandwidths of eachcomponent band.

Specifically, while in the common search space of a PDCCH signal of adownlink component band other than the basic component band, informationsize determination section 207 determines the basic information sizebased on the larger one of the information size of downlink assignmentcontrol information determined from the bandwidth of the target downlinkcomponent band in which the PDCCH signal is sent, and the informationsize of uplink assignment control information determined from thebandwidth of an uplink component band (which is not necessarily includedin the component band group of terminal 200) associated by the broadcastsignal in the target down link component band, in the UE specific searchspace, information size determination section 207 determines the basicinformation size based on the larger one of the information size ofdownlink assignment control information determined from the bandwidth ofthe target downlink component band and the information size of an uplinkassignment control information determined from the bandwidth of theuplink component band in the component band group of terminal 200.

As for a PDCCH signal of the basic component band, in both the commonsearch space and the UE specific search space, information sizedetermination section 207 determines the basic information size based onthe larger one of the information size of downlink assignment controlinformation determined from the bandwidth of the target downlinkcomponent band in which the PDCCH signal is sent, and the informationsize of uplink assignment control information determined from thebandwidth of an uplink component band in the component band group ofterminal 200.

Information size determination section 207 outputs information about thedecided basic information size and the PDCCH signal associated with thisinformation to PDCCH reception section 208.

PDCCH reception section 208 performs blind detection for a PDCCH signalbased on the basic information size decided in information sizedetermination section 207.

That is, PDCCH reception section 208 specifies the CRC bit part by usingthe basic information size (payload size) decided in information sizedetermination section 207. Next, after demasking the specified CRC bitpart using the terminal ID of terminal 200 in the UE specific searchspace, PDCCH reception section 208 determines the PDCCH signal as aPDCCH signal transmitted for terminal 200, if the CRC calculation resultis “OK” with respect to the whole PDCCH signal. However, since in acommon search space there is a possibility that both assignmentinformation for terminal 200 and assignment information to be receivedby a plurality of terminals (for example, scheduling information ofbroadcast signals) may be sent, in a common search space, PDCCHreception section 208 performs both damasking processes by the terminalID of terminal 200 and damasking process by an ID set in common betweena plurality of terminals, and executes the CRC calculation. Thus, thePDCCH signal decided to be received by terminal 200 is output to formatdetermination section 209.

Based on type information of assignment control information included ina PDCCH signal received from PDCCH reception section 208, formatdetermination section 209 determines whether the format of the PDCCHsignal is format 0 or format 1A. When determining as format 0, formatdetermination section 209 outputs uplink assignment control informationincluded in the PDCCH signal, to frequency mapping section 213. Also,when determining as format 1A, format determination section 209 outputsdownlink assignment control information included in the PDCCH signal, toPDSCH reception section 210.

Based on downlink assignment control information input from formatdetermination section 209, PDSCH reception section 210 extracts receiveddata from the PDSCH signal input from demultiplexing section 205.

Modulating section 211 modulates transmission data and outputs aresulting modulated signal to DFT (Discrete Fourier Transform) section212.

DFT section 212 converts a modulated signal input from modulatingsection 211 into a frequency domain, and outputs a resulting pluralityof frequency components to frequency mapping section 213.

In accordance with uplink assignment control information input fromformat determination section 209, frequency mapping section 213 maps aplurality of frequency components input from DFT section 212, on a PUSCHplaced in an uplink component band.

IFFT section 214 converts a mapped plurality of frequency componentsinto a time domain waveform, and CP adding section 215 adds a CP to thetime domain waveform.

RF transmission section 216 performs a radio transmission process (suchas an up-conversion and a digital-to-analog (D/A) conversion) to asignal with a CP, and transmits it through an antenna.

Next, an operation of base station 100 and terminal 200, which have theabove mentioned configurations, will be described. FIG. 6 is a view forexplaining operations of base station 100 and terminal 200.

In FIG. 6, base station 100 has two downlink component bands DB 1 and 2,and two uplink component bands UB 1 and 2, as the communication bands ofbase station 100. In FIG. 6, the bandwidths of UB 1 and DB 1 are 20 MHzand the bandwidths of DB 2 and UB 2 are 10 MHz. DB 1 forms a pair bandwith UB 1, DB 2 forms an uplink and a downlink pair bands with UB 2respectively. In these pair bands, base station 100 accommodatesconventional LTE terminals. Thus, base station 100 transmits in DB 1, aBCH including information about UB 1 and in DB 2 transmits a BCHincluding information about UB 2. By receiving a BCH, an LTE terminalcan recognize the relationships of an uplink component band and adownlink component band.

In FIG. 6, one uplink component band UB 1 is associated with twodownlink component bands DB 1 and DB 2 as component band groups of firstterminal 200. Here, a BCH that broadcasts the information about anuplink component band in a component band group of first terminal 200 istransmitted from DB 1, so that, as for first terminal 200, DB 1 is thebasic component band.

Base station 100 sets uplink component band UB 1 as uplink channelresource to first terminal 200, and downlink component bands DB 1 and 2as downlink channel resource. Thus, the component band group associatedwith first terminal 200 is formed by DB 1, 2 and UB 1.

Then, base station 100 includes uplink assignment control informationand downlink assignment control information into the PDCCH signal, andtransmits these to terminal 200. In FIG. 6, the arrow from a PDCCHtowards uplink data (UL Data) means that there is a possibility thatuplink assignment control information may be sent in the PDCCH. Also,the arrow from a PDCCH towards downlink data (DL Data) or a D-BCH meansthat there is a possibility that downlink assignment control informationmay be sent in the PDCCH.

Also, in information size adjusting section 103, the information size ofa PDCCH signal is adjusted if necessary. Specifically, with the basiccomponent band, information size determination section 103 adds zeroinformation to the smaller information size until the information sizeof downlink assignment control information determined from the bandwidthof the basic component band and the information size of uplinkassignment control information determined from the bandwidth of anuplink component band in the component band group of first terminal 200,have equal information size. As for downlink assignment controlinformation included in the common search space of the PDCCH signal sentwith a component band other than the basic component band, informationsize adjusting section 103 adjusts the information size by using thelarger one of the information size of downlink assignment controlinformation determined from the bandwidth of a downlink component bandin which the target downlink assignment control information is sent, andthe information size of uplink assignment control information determinedfrom the bandwidth of an uplink component band (which is not necessarilyincluded in the component band group of first terminal 200) associatedby the broadcast signal of the target downlink component band, as a sizeadjustment reference.

Meanwhile, the size of downlink assignment control information includedin the UE specific search space of a PDCCH signal sent by a componentband other than the basic component band is determined from thebandwidth of the downlink component band in which the target downlinkassignment control information is sent, and the bandwidth of the uplinkcomponent band of the component band group of terminal 200.

Here, the above size adjusting method will be described in detail usinga bandwidth of a component band shown in FIG. 6.

With DB 1 (the basic component band of first terminal 200) shown in FIG.6 the information size adjustment is performed using the relationshipsof the bandwidth of DB 1 and the bandwidth of UB 1 as mentioned above.Thus, the bandwidths of DB 1 and UB 1 are both 20 MHz, so that theinformation amount necessary to report an uplink assignment resource andthe information amount necessary to report a downlink assignmentresource become equal. However, as for the information other than aresource report that is necessary for assignment control, a downlink isslightly (approximately 1 bit) larger than an uplink. Thus, in both acommon search space and a UE specific search space of a PDCCH signal ofDB 1, information size adjustment is performed assuming that Format 0 ispadded slightly.

With DB 2 (a downlink component band other than the basic component bandof first terminal 200) shown in FIG. 6, as mentioned above, in a commonsearch space information size adjustment is performed using therelationships of the bandwidth of DB 2 and the bandwidth of UB 2, and ina UE specific search space information size adjustment is performedusing the relationships of the bandwidth of DB 2 and the bandwidth of UB1.

Thus, in the common search space of DB 2, both bandwidths of DB 2 and UB2 are 15 MHz, so that information size adjustment is performed assumingthat Format 0 is padded slightly.

Meanwhile, in the UE specific search space of DB 2, information sizeadjustment is performed assuming that Format 1A is padded substantially.This is because the bandwidth of UB 1 is 20 MHz, so that the informationamount to report uplink assignment resource necessary for UB 1 becomessignificantly larger than the information amount to report downlinkassignment resource necessary for DB 2. Thus, with DB 2, the informationsize (payload size) of PDCCH subject to blind detection in terminal 200is bigger in the UE specific search space than in the common searchspace.

In other words, the information size that is the size adjustmentreference of the common search space of DB 2 is small, so that it is notpossible to map uplink assignment control information for terminal 200to the common search space of DB 2 because the information size is notenough. By this means, in the configuration shown in FIG. 6, basestation 100 is controlled not to map uplink assignment controlinformation for terminal 200 to the common search space of DB 2. Notethat, this control of not mapping is for the case where both DB 2 and UB2 are smaller than UB 1. Meanwhile, for example, as shown in FIG. 7,when the bandwidth of UB 2 is 20 MHz as UB 1, even in the common searchspace of DB 2, information size adjustment is performed assuming thatFormat 1A is padded substantially, as in the UE specific search space.Thus, in this case, in the common search space, the information size ofthe PDCCH to which terminal 200 should perform blind detection, and thesize of an uplink assignment control information which is necessary toreport of UB 1 become equal, so that it becomes possible to transmituplink assignment control information even from the common search spaceof DB 2.

According to the present embodiment, base station 100 has a plurality ofuplink component bands and a plurality of downlink component bands as acommunication band of base station 100, sets for each radio terminal thecomponent band group formed by the uplink component band in thecommunication band and a plurality of downlink component bandsassociated with the target uplink component band, and is able tocommunicate with radio terminal 200 by using the component band group.Base station 100 is, for example, an LTE-A base station, and radioterminal 200 is, for example, an LTE-A terminal.

In base station 100, based on the size adjustment reference, informationsize adjusting section 103 adjusts the information sizes of uplinkcontrol information associated with an arbitrary target terminal anddownlink control information, which are included in a PDCCH signal.

Specifically, in the common search space of a downlink component band(that is, a downlink additional component band) other than the basiccomponent band but included in the component band group, informationsize adjusting section 103 uses the larger one of the information sizeof downlink assignment control information determined from the bandwidthof the downlink additional component band and the information size ofuplink assignment control information determined from the bandwidth ofthe uplink component band associated with the downlink additionalcomponent band by the broadcast signal (a BCH) sent in the downlinkadditional component band, as the size adjustment reference. Meanwhile,in the UE specific search space of the downlink additional componentband, information size adjusting section 103 uses the larger one of theinformation size of downlink assignment control information determinedfrom the bandwidth of the downlink additional component band and theinformation size of uplink assignment control information determinedfrom the bandwidth of the uplink component band of the component bandgroup, as the size adjustment reference. The pairs of the downlinkcomponent band and the uplink component band, which are associated withthe broadcast signal sent by this downlink component band, are also usedin the LTE system. Thus, this association is related to the associationin LTE. Meanwhile, the associations of a plurality of downlink componentbands (which include the basic component band and the downlinkadditional component band) and an uplink component band in the componentband group are individually associated with target terminals.

By setting as above, first, the UE specific search space individuallyassigned to each terminal can adopt the size adjustment referenceaccording to the association in the component band group set for thetarget terminal, and it is possible to make the information size ofdownlink assignment control information and the uplink assignmentcontrol information equal by the size adjustment based on this sizeadjustment reference. By this means, it is possible to reduce the numberof times of blind detection in the target terminal. Meanwhile, thecommon search space where scheduling information of broadcast signals issent can adopt the size adjustment reference according to the basicassociation. By this means, even in a terminal using the component bandpair according to the basic association, any problem on receivingbroadcast signals is not produced.

The above has been explained assuming that information about thedownlink additional component band in the component band group isnoticed from base station 100 to terminal 200 by a dedicated channel.However, the present invention is not limited to this, and, for example,it is equally possible to broadcast the information about a terminalband group using a BCH+, when a BCH (a BCH+) that only an LTE-A terminalcan receive is transmitted from base station 100, in addition to a BCHthat both an LTE terminal and an LTE-A terminal can receive.

As mentioned above, depending on the relationships of bandwidths of anuplink component band and a downlink component band, it is equallypossible to perform a control of not mapping the uplink frequencyassignment to the common search space of a downlink component band otherthan the basic component band. When performing this control, in thecommon search space, only downlink frequency assignment is mapped, sothat type information (Format indicator (1 bit)) of assignment controlinformation that is usually included is unnecessary. Thus, it is equallypossible to transmit a parity bit or to transmit other information byusing the resource that is prepared to map type information ofassignment control information.

According to the above explanation, in a UE specific search space of adownlink additional component band other than the basic component band,uplink assignment control information is reported. However, the presentinvention is not limited to this, and it is equally possible todetermine the information size of a PDCCH in the UE specific searchspace of a downlink additional component band, only from the informationsize of downlink assignment control information determined from thebandwidth of the downlink additional component band, when uplinkassignment information is not reported in the downlink component bandother than the basic component band. By this means, it is possible toavoid unnecessary padding for uplink assignment control information(format 0).

The embodiment mentioned above explains an example when the presentinvention is performed by hardware, but the present invention can beimplemented with software.

Furthermore, each function block employed in the description of theaforementioned embodiment may typically be implemented as an LSIconstituted by an integrated circuit. These may be individual chips orpartially or totally contained on a single chip. “LSI” is adopted herebut this may also be referred to as “IC,” “system LSI,” “super LSI,” or“ultra LSI” depending on differing extents of integration.

Further, the method of circuit integration is not limited to LSI's, andimplementation using dedicated circuitry or general purpose processorsis also possible. After LSI manufacture, utilization of an FPGA (FieldProgrammable Gate Array) or a reconfigurable processor where connectionsand settings of circuit cells in an LSI can be regenerated is alsopossible.

Further, if integrated circuit technology comes out to replace LSI's asa result of the advancement of semiconductor technology or a derivativeother technology, it is naturally also possible to carry out functionblock integration using this technology. Application of biotechnology isalso possible.

The disclosure of Japanese Patent Application No. 2009-059501, filed onMar. 12, 2009, including the specification, drawings and abstract, isincorporated herein by reference in its entirety.

INDUSTRIAL APPLICABILITY

A radio terminal, radio base station, channel signal forming method andchannel signal reception method of the present invention is useful toreduce the number of times of blind detection in a reception process ofassignment control information without causing any problems on receivingbroadcast signals.

The invention claimed is:
 1. A base station communicating with a userequipment (UE), for which an uplink component carrier and a plurality ofdownlink component carriers are configured, the base station comprising:an adjusting section configured to adjust a payload size of controlinformation, which is transmitted in a downlink control channel, basedon a basic payload size; and a multiplexing section configured to mapthe control information onto a search space in at least one of theplurality of downlink component carriers, wherein: the plurality ofdownlink component carriers include a primary downlink componentcarrier; the basic payload size of the control information mapped onto asearch space in the primary downlink component carrier is a payloadsize, which is given based on a number of information bits obtained froma bandwidth of the primary downlink component carrier, and on a numberof information bits obtained from a bandwidth of the uplink componentcarrier, the bandwidth of the uplink component carrier being broadcastedin the primary downlink component carrier; and the basic payload size ofthe control information mapped onto a search space in a downlinkcomponent carrier other than the primary downlink component carrier is apayload size, which is given based on a number of information bitsobtained from a bandwidth of the downlink component carrier other thanthe primary downlink component carrier.
 2. The base station according toclaim 1, wherein the primary downlink component carrier is a downlinkcomponent carrier that broadcasts information related to the uplinkcomponent carrier configured for the UE.
 3. The base station accordingto claim 1, wherein: the search space is a common search space or a UEspecific search space; the basic payload size of the control informationmapped onto the common search space or the UE specific search space inthe primary downlink component carrier is a payload size, which is givenbased on the number of information bits obtained from the bandwidth ofthe primary downlink component carrier, and on the number of informationbits obtained from the bandwidth of the uplink component carrier, thebandwidth of the uplink component carrier being broadcasted in theprimary downlink component carrier; and the basic payload size of thecontrol information mapped onto the UE specific search space in adownlink component carrier other than the primary downlink componentcarrier is a payload size, which is given based on the number ofinformation bits obtained from the bandwidth of the downlink componentcarrier other than the primary downlink component carrier.
 4. The basestation according to claim 1, wherein the basic payload size of thecontrol information mapped onto the search space in the primary downlinkcomponent carrier corresponds to a larger one of the number ofinformation bits obtained from the bandwidth of the primary downlinkcomponent carrier and the number of information bits obtained from thebandwidth of the uplink component carrier, the bandwidth of the uplinkcomponent carrier being broadcasted in the primary downlink componentcarrier.
 5. The base station according to claim 1, wherein the controlinformation includes at least one of downlink assignment information anduplink assignment information; the basic payload size of the controlinformation mapped onto the search space in the primary downlinkcomponent carrier is a payload size, which is given based on a number ofinformation bits in downlink assignment information obtained from thebandwidth of the primary downlink component carrier, and on a number ofinformation bits in uplink assignment information obtained from thebandwidth of the uplink component carrier, the bandwidth of the uplinkcomponent carrier being broadcasted in the primary downlink componentcarrier; and the basic payload size of the control information mappedonto the search space in a downlink component carrier other than theprimary downlink component carrier is a payload size, which is givenbased on a number of information bits in downlink assignment informationobtained from the bandwidth of the downlink component carrier other thanthe primary downlink component carrier.
 6. The base station according toclaim 5, wherein the multiplexing section maps the downlink assignmentinformation onto the search space in at least one of the plurality ofdownlink component carriers, and maps the uplink assignment informationonto the search space in the primary downlink component carrier.
 7. Thebase station according to claim 6, wherein the uplink assignmentinformation is not mapped onto the search space in a downlink componentcarrier other than the primary downlink component carrier.
 8. The basestation according to claim 5, wherein the adjusting section adjusts thepayload size of the downlink assignment information mapped onto thesearch space in the primary downlink component carrier and the payloadsize of the uplink assignment information mapped onto the search spacein the primary downlink component carrier to be equal to each other. 9.The base station according to claim 5, wherein the adjusting sectionappends zeros to one of the downlink and uplink assignment informationmapped onto the search space in the primary downlink component carrier,which includes the number of information bits that is smaller than thenumber of information bits included in the other of the downlink anduplink assignment information, until the payload size of said one of thedownlink and uplink assignment information becomes equal to the payloadsize of said other of the downlink and uplink assignment information.10. The base station according to claim 5, wherein a format of thedownlink assignment information is format 1A, and a format of the uplinkassignment information is format
 0. 11. A method for forming a controlchannel at a base station communicating with a user equipment (UE), forwhich an uplink component carrier and a plurality of downlink componentcarriers are configured, the method comprising: adjusting a payload sizeof control information, which is transmitted in a downlink controlchannel, based on a basic payload size; and mapping the controlinformation onto a search space in at least one of the plurality ofdownlink component carriers, wherein: the plurality of downlinkcomponent carriers include a primary downlink component carrier; thebasic payload size of the control information mapped onto a search spacein the primary downlink component carrier is a payload size, which isgiven based on a number of information bits obtained from a bandwidth ofthe primary downlink component carrier, and on a number of informationbits obtained from a bandwidth of the uplink component carrier, thebandwidth of the uplink component carrier being broadcasted in theprimary downlink component carrier; and the basic payload size of thecontrol information mapped onto a search space in a downlink componentcarrier other than the primary downlink component carrier is a payloadsize, which is given based on a number of information bits obtained froma bandwidth of the downlink component carrier other than the primarydownlink component carrier.
 12. The method for forming a control channelaccording to claim 11, wherein the primary downlink component carrier isa downlink component carrier that broadcasts information related to theuplink component carrier configured for the UE.
 13. The method forforming a control channel according to claim 11, wherein: the searchspace is a common search space or a UE specific search space; the basicpayload size of the control information mapped onto the common searchspace or the UE specific search space in the primary downlink componentcarrier is a payload size, which is given based on the number ofinformation bits obtained from the bandwidth of the primary downlinkcomponent carrier, and on the number of information bits obtained fromthe bandwidth of the uplink component carrier, the bandwidth of theuplink component carrier being broadcasted in the primary downlinkcomponent carrier; and the basic payload size of the control informationmapped onto the UE specific search space in a downlink component carrierother than the primary downlink component carrier is a payload size,which is given based on the number of information bits obtained from thebandwidth of the downlink component carrier other than the primarydownlink component carrier.
 14. The method for forming a control channelaccording to claim 11, wherein the basic payload size of the controlinformation mapped onto the search space in the primary downlinkcomponent carrier corresponds to a larger one of the number ofinformation bits obtained from the bandwidth of the primary downlinkcomponent carrier and the number of information bits obtained from thebandwidth of the uplink component carrier, the bandwidth of the uplinkcomponent carrier being broadcasted in the primary downlink componentcarrier.
 15. The method for forming a control channel according to claim11, wherein the control information includes at least one of downlinkassignment information and uplink assignment information; the basicpayload size of the control information mapped onto the search space inthe primary downlink component carrier is a payload size, which is givenbased on a number of information bits in downlink assignment informationobtained from the bandwidth of the primary downlink component carrier,and on a number of information bits in uplink assignment informationobtained from the bandwidth of the uplink component carrier, thebandwidth of the uplink component carrier being broadcasted in theprimary downlink component carrier; and the basic payload size of thecontrol information mapped onto the search space in a downlink componentcarrier other than the primary downlink component carrier is a payloadsize, which is given based on a number of information bits in downlinkassignment information obtained from the bandwidth of the downlinkcomponent carrier other than the primary downlink component carrier. 16.The method for forming a control channel according to claim 15, whereinthe mapping of the control information includes mapping the downlinkassignment information onto the search space in at least one of theplurality of downlink component carriers, and mapping the uplinkassignment information onto the search space in the primary downlinkcomponent carrier.
 17. The method for forming a control channelaccording to claim 16, wherein the uplink assignment information is notmapped onto the search space in a downlink component carrier other thanthe primary downlink component carrier.
 18. The method for forming acontrol channel according to claim 15, wherein the adjusting of thepayload size of the control information includes adjusting the payloadsize of the downlink assignment information mapped onto the search spacein the primary downlink component carrier and the payload size of theuplink assignment information mapped onto the search space in theprimary downlink component carrier to be equal to each other.
 19. Themethod for forming a control channel according to claim 15, wherein theadjusting of the payload size of the control information includesappending zeros to one of the downlink and uplink assignment informationmapped onto the search space in the primary downlink component carrier,which includes the number of information bits that is smaller than thenumber of information bits included in the other of the downlink anduplink assignment information, until the payload size of said one of thedownlink and uplink assignment information becomes equal to the payloadsize of said other of the downlink and uplink assignment information.20. The method for forming a control channel according to claim 15,wherein a format of the downlink assignment information is format 1A,and a format of the uplink assignment information is format 0.